1. Field of the Invention
This invention relates to a variable capacity wobble plate compressor in which the piston stroke length changes according to the inclination of a wobble plate.
2. Description of the Prior Art
FIGS. 1 and 2 show the whole arrangement of a conventional variable capacity wobble plate compressor. FIG. 1 shows the compressor in the full stroke condition, while FIG. 2 shows the compressor in the minimum stroke condition.
As shown in FIG. 1, the conventional variable capacity wobble plate compressor includes a thrust flange 140, a drive hub 141, a wobble plate 110, a coil spring 144 which functions as a destroke spring for decreasing the piston stroke length, and a coil spring 147 and a set of coned disk springs 146 which cooperate to function as a stroke spring for increasing the piston stroke length.
The thrust flange 140 is rigidly fitted on a drive shaft 105, for rotation in unison with the same.
The drive hub 141 is mounted on the drive shaft 105 via a hinge ball 109 axially slidably fitted on the drive shaft 105. Further, the drive hub 141 is tiltably connected to the thrust flange 140 via a linkage 142, for rotation in unison with the thrust flange 140.
The wobble plate 110 is slidably mounted on a boss of the drive hub 141, for performing wobbling motion as the drive hub 141 rotates. Further, the wobble plate 110 has each piston 107 connected thereto by a connecting rod 111, and the piston 107 reciprocates within a cylinder bore 106 associated therewith according to the axial wobbling motion of the wobble plate 110.
The coil spring 144 as a destroke spring is fitted on the drive shaft 105 between a front-side end of the hinge ball 109 and the boss of the thrust flange 140, for urging the hinge ball 109 in a direction of decreasing the inclination of the wobble plate 110 to thereby reduce the volume of a compression chamber within the cylinder bore 106.
The coil spring 147 and the set of coned disk springs 146 as the stroke spring are fitted on the drive shaft 105 in series between a rear-side end of the hinge ball 109 and a fixed washer 145 rigidly fitted on the drive shaft 105, for urging the hinge ball 109 in a direction of increasing the inclination of the wobble plate 110 to thereby increase the volume of the compression chamber within the cylinder bore 6.
In the variable capacity wobble plate compressor, as pressure within the crankcase 108 decreases, the inclination angle of the wobble plate 110 increases, so that an abutment portion 141c of the drive hub 141 abuts on a drive hub-receiving surface 140c (best shown in FIG. 2) formed on the thrust flange 140, as shown in FIG. 1. At this time, the coil spring 144 is contracted, whereas the coil spring 147 and the set of coned disk springs 146 are expanded, whereby the compressor is placed into the full stroke condition (the maximum delivery quantity condition in which the length of stroke of the piston 107 becomes the maximum).
On the other hand, as the pressure within the crankcase 108 increases, the inclination angle of the wobble plate 110 decreases, so that the abutment portion 141c of the drive hub 141 moves away from the drive hub-receiving surface 140c of the thrust flange 140 as shown in FIG. 2. At this time, the coil spring 144 is expanded, whereas the coil spring 147 and the set of coned disk springs 146 are contracted. When the axial length of the set of coned disk springs 146 becomes the minimum (i.e. the pitch becomes zero), the drive hub 141 stops tilting or rising toward the rear side of the compressor, whereby the compressor is placed into the minimum stroke condition (the minimum delivery quantity condition in which the length of stroke of the piston 107 becomes the minimum).
When the compressor is in the full stroke condition, however, the drive hub-receiving surface 140c of the thrust flange 140 has a reaction force of compression of the piston 107 applied thereto as long as the abutment portion 141c of the drive hub 141 and the drive hub-receiving surface 140c of the thrust flange 140 are in contact with each other after the abutment portion 141c abuts on the drive hub-receiving surface 140c, which causes slight vibrations of contact portions of the abutment portion 141c and the drive hub-receiving surface 140c. As a result, the vibrations can cause abrasion of the contact portions of the abutment portion 141c and the drive hub-receiving surface 140c.
Further, the reaction force of compression of the piston 107 applied to the drive hub-receiving surface 140c of the thrust flange 140 can deform the drive hub-receiving surface 140c or even cause breakage of the thrust flange 140 itself.
To prevent the above-mentioned abrasion, it is required to increase the hardness of the contact portions of the abutment portion 141c and the drive hub-receiving surface 140c e.g. by induction hardening. However, if this treatment is carried out, the number of man-hours as well as manufacturing costs of the compressor are increased.
Further, if the thrust flange 140 is reinforced so as to prevent deformation and breakage of the same, its dynamic balance is lost, which causes vibrations and untoward noises.
On the other hand, in the minimum stroke condition of the compressor, the inclination angle of the drive hub 141 becomes the minimum when the axial length of the set of coned disk springs 146 becomes the minimum to cause the set of coned disk springs 146 to exert its force as a stopper to the full. Therefore, bending stress of the coned disk springs 146 is extremely increased, which can cause breakage of the coned disk springs 146 or produce untoward noises.